AU2002239312B2

AU2002239312B2 - Low gloss powder coatings

Info

Publication number: AU2002239312B2
Application number: AU2002239312A
Authority: AU
Inventors: Owen H. Decker; M. Aaron Sparks
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 2000-11-21
Filing date: 2001-11-16
Publication date: 2007-04-26
Anticipated expiration: 2021-11-16
Also published as: NO20032211L; CA2423080A1; JP2004514761A; NO20032211D0; US6737467B1; CZ20031312A3; EP1345996A2; KR20030055312A; DE60112967T2; RU2268908C2; CN1476472A; WO2002042386A2; HUP0400550A2; SK5872003A3; PL362010A1; US20030125445A1; ES2247186T3; AU3931202A; MXPA03004434A; WO2002042386A3

Abstract

UV curable powder coating compositions containing 5 to 60 wt % spherical or near spherical particles having a median diameter of greater than 10, and most preferably greater than 15 microns, which refract and scatter applied UV light in all directions through the coating layer during curing to enhance the through-cure properties of the resulting coating.

Description

WO 02/42386 PCT/US01/43789 TITLE OF INVENTION Low GLOSS POWDER COATINGS Field of the Invention The invention relates to powder coatings in general and, more specifically, to powder coatings that provide a low gloss appearance to the coated article.

Background of the Invention Powder coatings are widely used to provide a decorative and/or protective coating on substrates. They are becoming increasingly popular because they are applied in a solid state or slurry. These application states mean that the powder coatings use little or no solvents, unlike their conventional liquid coating counterparts. In addition, solid state application permits the powder to be collected, purified and re-used.

In certain applications, it is necessary or desirable for the powder coating to have a surface that is smooth in appearance, but has a low gloss or shine. Such applications are those where low gloss is aesthetically desired, or where glare from the coating surface can interfere with the safe or proper use of the coated article, such as firearms, optical devices, military applications and motor vehicles, aircraft and other vehicles. Prior art attempts to control gloss in powder coatings has taken three different approaches using fillers, waxes and differential cure.

The addition of fillers is known to reduce the gloss of powder coatings. Indeed, gloss reduction is an unavoidable, and often undesirable, side effect of filler addition. For example, the 3M Company markets ceramic microspheres under the trade name ZeeospheresTM for use in powder coatings to control gloss. A filler commonly used for gloss control is wollastonite, whose needle-shaped crystals are very effective at reducing gloss by reducing the microscopic smoothness of coatings. Fillers of other shapes are also commonly used to reduce gloss. The shortcoming of the use of fillers to control gloss is that their addition also reduces coating flow, typically increasing the amount of waviness or texture known as "orange peel." Hydrocarbon and fluorocarbon waxes are used to reduce the gloss of powder coatings. As a wax-containing coating is baked, the wax migrates to the coating/air interface where it forms a layer with reduced gloss. Shortcomings of this approach are that the wax softens the coating surface and reduces its resistance to marring, staining and chemical attack.

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O Another way to reduce gloss, which is especially effective with expoxy and epoxy/polyester hybrid coatings, is to incorporate at least two curing agents or two Z differently structured or differently-catalyzed resins. Upon incomplete molecular IN mixing, such as is typically encountered in a powder coating extruder, these differential-cure systems result in the development of zones of varying shrinkage or r varying surface tension on the coating surface during cure, yielding a Cc microscopically-rough layer which is seen as low gloss.

(Ni N The use of a finely milled polyester powder as a gloss reducing agent is described in WO 00/01774. However, that application does not disclose that spheroidal shaped particles and other gloss reducing agents other than polyesters, such as glass or ceramic microspheres, spheroidal minerals or metal microspheres, can be successfully incorporated into powder coating compositions as low gloss additives, in order to produce coated surfaces that are both smooth in appearance, as well as, low in gloss or shine.

08 361 describes the use of spherically shaped non-reactive polymer particles for producing matt finishes. That application, however, never discloses that particles other than polymer particles, such as glass or ceramic microspheres, spheroidal minerals or metal microspheres, can be added to powder coating compositions to produce coated surfaces that are both smooth in appearance, as well as, low in gloss or shine.

Variations of this approach are widely used. A shortcoming of this approach is that coating properties such as impact resistance, flexibility, or chemical resistance suffer.

Summary of the Invention In one aspect, the invention provides an improved powder coating composition, the improvement wherein comprising the use in the composition of spheroidal particles having a median particle size greater than 10 microns and preferably greater than microns, and having a maximum particle size of about 50 microns.

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In another embodiment, the invention provides a process of reducing gloss in a powder coating, the process comprising adding speriodical particles to a powder

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Z coating composition, wherein said spheroidal particles have a median particle size N greater than 10 microns and preferably greater than 15 microns, and have a maximum particle size of about 50 microns.

C€ These and other features of the invention will become apparent on a further reading Cc of the application.

IC Detailed Description of the Embodiments The powder coatings of this invention provide the formulator with an opportunity to control the gloss of the final coating while minimizing or eliminating the negative effects of the prior art attempts at controlling gloss; loss of coating flow and creation of "orange peel" surface effects. It is important to note that the coatings of this invention have a rough or textured surface microscopically, but otherwise appear smooth to the naked eye.

The powder coating compositions of this invention contain one or more thermosetting or thermoplastic resins commonly used in such coatings and well known in the art. Such resins include those based on epoxy, polyester, acrylic and/or urethane resins. Examples of such resins include saturated and unsaturated polyesters, acrylics, acrylates, polyester-urethanes, acrylic-urethanes, epoxy, epoxypolyester, polyester-acrylics and epoxy-acrylics. Useful thermoplastic resins may include nylon, polyvinylchloride, polyethylene, polyethylene terephthalate, polybutylene terephthalate and polypropylene, for example.

The powder coating compositions of this invention may be applied by electrostatic spray, thermal or flame spraying, or fluidized bed coating methods, all of which are known to those skilled in the art. The coatings may be applied to metallic and/or non-metallic substrates. Following deposition of the powder coating to the desired thickness, the coated substrate is typically heated to melt the composition and cause it to flow. In certain applications, the part to be coated may be pre-heated before the application of the powder, and then either heated after the application of the powder 16/ 1/06,ck 13280nov I Ospeci,3 -4-

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or not. Gas or electrical furnaces are commonly used for various heating steps, but other methods microwave) are also known. Curing cross-linking) of the Z coating may be carried out by thermal or photochemical methods ultraviolet radiation, infrared radiation, etc.). Curing may be effected by heat conduction, convection, radiation or any combination thereof.

Cc The powder coating compositions of this invention contain spheroidal particles. The Cc term "spheroidal" as used herein means generally spherical in shape. More specifically, the term means filler materials than contain less than 25% particle agglomerates or fractured particles containing sharp or rough edges. The spheroidal particles should be non-reactive or inert so as not to interfere with the other properties of the composition. Examples of suitable spheroidal particles are glass microspheres, ceramic microspheres, naturally-occurring or synthetic spheroidal minerals such as cristobalite, polymer microspheres and metal microspheres.

As already mentioned, the spheroid particles must have a median particle size greater than 10 microns, preferably of greater than 15 microns. Intermediate ranges are included. As the mean particle diameter decreases, the surface per unit weight increases. The increase in surface area results in a tendency of the filler to dry the coating, reduce flow, and induce roughness in the coating. As indicated in the working examples, spheroidal particles having a median diameter of 10 microns or below produced only marginal results in gloss control, whereas at median diameters greater than 10, particularly of greater than 15, the spheroidal particles have good results.

The upper limit of the diameter of the spheroidal particles is dependent on the intended thickness of the final coating in that the particles must have a diameter less than the coating thickness. Most powder coatings, especially "decorative" powder coatings, are designed to be applied at a dry film thickness of about 50 microns.

Thus, in most applications, the spheroidal particles should have a maximum diameter of less than about 50 microns, preferably 40 microns.

16/I 1/06ck 13280nov I Ospeci,4 Snternational Application No.: PCT/US01/43789 International Filing Date: 16 November 2001 Replacement page The spheroidal particles may be present in the composition in an amount of from wt% to 60 wt%, based on the total weight of the powder coating composition. Below wt%, little effect on gloss is observed. Above 60 wt%, an unacceptable loss of coating flow results. It is understood that these are general guidelines and the exact weight of spheroidal particles will depend on the specific gravity of the spheroidal particles, the degree of gloss reduction desired and the other components of the powder coating composition.

In addition to the resins and spheroidal particles, the powder coating compositions of this invention may contain other additives that are conventionally used in powder coating compositions. Examples of such additives include fillers, extenders, flow additives, catalysts, hardeners and pigments. Compounds having anti-microbial activity may also be added as is taught in US 6,093,407, the entire disclosure of which is incorporated herein by reference.

The powder coatings of this invention are prepared by conventional manufacturing techniques used in the powder coating industry. For example, the ingredients used in the powder coating, including the spheroidal particles, can be blended together and heated to a temperature to melt the mixture and then extruded. The extruded material is then cooled on chill rolls, broken up and then ground to a fine powder.

The spheroidal particles may also be combined with the coating powder after it is formed in a process known as "bonding." In this process, the coating powder and the material to be "bonded" with it are blended and subjected to heating and impact fusion to join the differing particles.

P rinted: 23-01 -2003' ~DESH 01 1987056-U SO 143789! international Application No.: PCTiUS01/43789 International Filing Date: 16 November 2001 Replacement page 6

EXAMPLES

Table 1 identifies a number of commercially available spheroidal particles and characterizes their usefulness as gloss control agents in powder coating compositions.

TABLE I SPHEROIDAL GLOSS CONTROL

AGENTS

Glass Microspheres (Potters Industries, Inc, Valley Forge, PA) GRADE MAX. DIA. (pm) Spheriglass'~' 3000E 90% 5 60 pm Sphe riglas 3T 3000E 45 screened. at 45 PM SpheglassT

CQ

Ceramic Microspheres (3M C MEDIAN UIA. (pm) EDIAN DIA. (pm) 35 High' 23 High 3 Low (too fine) orporation, Minneapolis, h G200 ZeeospheresTI 12 G6400 Zeeospheresw 24 G600 Zeeospheres~' 40 Wq610 Zeeospheres~m 40 G800 Zeeospheres m 200 G850 ZeeospheresTIA 200 G850 ZeeospheresA 45 screened at 45 pm Cristobalite Process Minerals, GoresiI~m C-400 100 GoresiI~m 1045 4 Low _(too fine) 5 low (too fine) 6 Low (too fine) 10 Marginal (too fine) 18 High' 40 Hig-hi 20 High Inc., Akron, OH)- 9~ Low (too fine) 1 Marginal (too fine) Goresil~m 835 35 I jLow (oo Tine) 552 1 Low (too fine) I f~+ Goresilm 215 1b I

I

Z. VWV UW .j Notes: 1. Useful only for coatings of thickness greater than about 50 microns..

Examples 1-8 The following examples illustrate the importance of the proper filler particle size on gloss control and coating smoothness. The spheroidal fillers listed in Table 3 -were tested in the composition listed below in Table 2: Priinted '23 -01-'2003i DESC01987056-USO143789 International Application No.: PCT/US01143789 International Filing Date: 16 November 2001 Replacement page 7 TABLE 2 TGIC-CURED POLYESTER COMPOSITION

I.

I

Component Crylcoat 2988 Polyester Resin (UCB) Araldite PT-810 Curing Agent (Vantico) Modaflow III Flow Aid (Solutia) Benzoin Degassing Aid (Estron) R-960 TiOz Pigment (DuPont) Raven 450 Pigment (Columbia) Spheroidal Particle Parts by weight 100 1.3 8.1 0.65 See Tables 3 and 4 Powder coating compositions were prepared by combining and bag-blending the components, followed by melt-extrusion. Extrudate was solidified between chilled rolls, then broken up and ground to powder. Powders were scalped at 80 mesh (180 microns) to remove coarse particles.

Coatings were prepared by applying the powdered compositions to 0.032 inch (0.081 cm) thick grounded steel panels using an electrostatic spray gun, then by baking the .powder-coated panels for 10 minutes at 400°F (204*C). The thickness of the powder coatings was approximately 50 microns.

After cooling, the coatings were evaluated for gloss and smoothness. These results appear in Table 3.

Printed:23-01-2003 DESC 01987056-US0143789 International Application No.: PCT/US01/43789 International Filing Date: 16 November 2001 Replacement page 8 COATING COMPOSITIONS Examples Spheroidal Particle 1 2 3 4 5 6 7 8 Screened' Spheriglass' 20 40 60 3000E (phr 2 G-400 Zeeospheres (phr) 20 40 Screened' G-850 Zeeospheres T (phr) Properties Gloss 102 74 50 38 75 68 60 PrI cmnnthness 3 6 7 7 7 7 6 6 7 Inclined Pla 300°F (149 Pencil Hare MEK Resis Direct Imp te Flow (mm) at 82 75 67 55 68 54 43 48 i°C) dness 4 H H H H H H H H tance 5 5 5 5 5 5 5 act Resistance 6 60 80 80 80 Notes: Particles were screened to remove particles larger than 45 pm.

"phr" means parts per hundred parts resin.

PCI Smoothness: By comparison to standards from 1 (heavy orange peel) to (smooth).

In order of increasing hardness: 2B, B, HB, H, 2H, 3H, etc.

Rub-off noted upon 50 double rubs with a methyl ethyl ketone-saturated cotton swab, from 1 (rub through) to 5 (no effect).

Inch-lb impact which did not result in cracking using a YA" hemispherical tup.

Discussion of Results Example 1. This example (Control) shows the high gloss of an unmodified coating.

Examples 2 and 5. Each of these examples contained 20 phr (14.5 wt%) of spheroidal particles, but of different sizes. In both instances, gloss was reduced to about the same level (74 vs. 75). However, the loss of flow in example 5 was significantly higher than in example 2, which is attributed to the fact that the spheroidal particles in example 5 had a median diameter of 5 pm, which is at the lowest end of the acceptable range.

SInternational Application No.: PCT/US01/43789 International Filing Date: 16 November 2001 Replacement page 9 Examples 3 and 6. Each of these examples contained 40 phr (25.3 wt%) of spheroidal particles, but of different sizes. The spheroidal particles in example 3 were more effective at reducing gloss (50 vs. 68) and also had less of a negative effect on flow (67 vs. 54 mm). These results are attributed to the fact that the, spheroidal particles used in example 6 had a median diameter of 5 pm, which is below the acceptable range.

Examples 4, 7 and 8. The spheroidal particles in each of these examples comprised phr (33.7 wt%) of the composition. The spheroidal particles in examples 4 and 8 were about equally effective in gloss reduction (38 and 35, respectively) and were much better than the particles used in example 7 The data also show that the glass particles had less of a negative impact on flow versus the ceramic particles of approximately equal size (example 4 vs. example A comparison of examples 7 and 8 demonstrates again that finer particles have a greater effect on flow reduction.

Pencil Hardness Comparison of Examples 2-7 with Example I (control) showed that the addition of the spheroidal particles does not reduce pencil hardness, a measure of mar resistance.

MEK Resistance Comparison of Examples 2-7 with Example 1 (control) showed that the addition of the spheroidal particles does not reduce MEK resistance.

Impact Resistance Comparison of Examples 2-4 and 8 with Example 1 (control) showed that the addition of the spheroidal particles has no negative effect on impact resistance.

Examples 9-13 Coatings were prepared, coated and evaluated as in the above examples using the spheroidal particles identified in Table 4.

812003 Printed:23-01 -2003 DE ISC 019870567USO143789 International Application No.: PCT/US01/43789 International Filing Date: 16 November 2001 Replacement page TABLE 4 COATING COMPOSITIONS Spheroidal Particles Example 1 9 10 11 12 13 GoresilTm 215 (phr) 60 Goresil T 525 (phr) 60 Goresilm 835 (phr) 60 GoresilT 1045 (phr) 60 Goresil T C-400 (phr)- Max. Particle Size N/A 15 25 35 45 100 Median Particle Size (pm) N/A 2 5 8 10 9 Gloss 96 66 59 52 42 43 Inclined Plate Flow (mm) at 91 21 25 29 .32 31 375 0 F (149 0

C)

Smoothness 6 1 1 2 3 11 Notes: This coating exhibited "seeds" due to filler particles greater than the thickness of the coating.

Discussion of Results Example 1. This example showed the high gloss of an unmodified control coating.

Gloss and Median Particle Size Examples 9 through 12. As the median particle size increased from 2 to 10, the particles became more effective at reducing gloss.

Gloss fells from 66 at 2 microns to 42 at 10 microns.

Flow and Median Particle Size Examples 9 through 12. As the median particle size increased from 2 to 10, the particles had less effect on.flow. Flow rose from 21 mm at 2 microns to 32 mm at 10 microns.

170 i 2,003 Prited,23-O1 -2O0,3' DESo 0o,1987056-US0143789 International Application No.: PCTIUSO14:3789 International Filing Date: 16 November 2001 Replacement page 11 Smoothness and Median Particle Size Examples 9 through 12. As the median particle size increased from 2 to 10, the coating became smoother. Smoothness rose from a rough 1 at 2 microns to less-rough 3 at 10 microns.

Smoothness and Maximum Particle Size Example 13. This example showed the "seeds" which result from the presence of particles larger than the thickness of the coating (approx. 50 microns).

The conclusion from these examples is that best results with cristobalite spheroidal particles were obtained with samples which had the highest available median particle size, so long as no particles were thicker than the thickness of the coating.

Examples 14-19 These examples demonstrate that a properly-sized spherical filler can reduce the gloss of a variety of different coating types. Tables 5-8 list the components of the coatings that were prepared, along with gloss, smoothness and flow results. Results are summarized in Table 9.

TABLE ANHYDRIDE-CURED EPOXY COATING COMPOSITION Examples Component 14 DER 6225 Epoxy Resin (DOW) 100 100 Benzophenonetetracarboxylic anhydride 15 (Jayhawk Fine Chemical) Zinc neodecanoate (Shepherd Chemical) 0.5 R-706 TiO2 Pigment (DuPont) 50 Modaflow III (Solutia) 1.3 1.3 Benzoin (Estron) 0.5 Spheriglass 3000E (PQ Corp.) screened at 45 pm Properties Gloss (600) 112 54 Smoothness (PCI) 8 7-8 Inclined Plate Flow (mm) at 300°F 20 (149C) E-0-w12i003 6-VO-LOOZ (P-ri-Ak) aisaVL:6L OWlllj ~lngdl Aq peA!e3a8 ZZ99L9O-lfl9S :oNG\j SNOS 12- TABLE 6 EP0XYIP0LYESTE HYB3RID COAM1NG COMI'osmow Examples Copnet16 17 Uralac P 5998 Polyester (OSM) 50. DER 662U Epoxy Resin (DOW) so R-7aO T102 Pigment (DuPont) 50 Modafiow III (Soluia) 1.3- 1.3 Berizoin (Estron) 0.5 SpheriglassThl 3000E (PQ Corp.) s0 screened at 45 pim aas(o! Properties 105__ 39 Smoothness (PCf} 9 8-9_ Inclined Plate Flow (mm) at SO 0 F88 3 TABLE 7 POLYESTER URE-7HANE COAniNG COMPOSITON Examples Component 18 1is Rucote 102 HYD Pcilyester Resin (Ruco) 10010 Alcure 4400 Blocked Isocyanafte 25 _(McWhorter) R-706 T102 Pigment (IPuPont) 50 Modaflow III (Salutia) 1.3 1.3 Benzoin (Estron) 0.5 SpheviglasslA 300QE (PQ Corp.) s0 sceehed at 45 rn Properties Glass (6006) gg 3 Smootness (PCI1) 8 Inclined Plate Flow (mm) at 3007 0 F 7 SOO/GOOM soo/socl~haumvq ?NNI'IqMo RIGt 6G26 E tS+ xva CI'.6I DEL LOCZ EO/6Z 13- Table 9 COATING SURVEY SUMMARY Chemistry Example Gloss Flow Smoothness TGIC Polyester 1 (control) 102 82 6 4 38 55 7 Anhydride Epoxy 14 (control) 112 20 8 54 20 7-8 Hybrid 16 (control) 105 88 9 17 39 34 8-9 Urethane 18 (control) 99 95 8 19 31 77 8 These data show that properly-sized spherical fillers can be reliably used to reduce gloss in a variety of powder coating chemistries.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form or suggestion that the prior art forms part of the common general knowledge in Australia.

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Claims

1. A low gloss powder coating composition comprising spheroidal particles and at least one resin selected from the group consisting of thermosetting resins and thermoplastic resins, wherein said spheroidal particles comprise 5 to 60 wt. of the coating composition and have a median particle diameter greater than 10 microns C, and a maximum particle diameter of 50 microns, further wherein said spheroidal Sparticles are selected from the group consisting of glass microspheres, ceramic CM microspheres, spheroidal minerals and metal microspheres.

2. The coating of claim 1, wherein the spheroidal particles have a median diameter greater than 15 microns.

3. The coating composition of claim 1 or 2 wherein said resin is selected from the group consisting of saturated polyesters, unsaturated polyesters, acrylic resins, acrylate resins, polyester-urethanes, acrylic-urethanes, epoxy, epoxy-polyester, polyester-acrylics, epoxy-acrylics, polyamides, polyvinylchloride, polyethylene, polyethylene terephthalate, polybutylene terephthalate and polypropylene,

4. The coating composition of any one of claims 1 to 3 wherein the spheroidal particles comprise W610, G800 or G850 zeeospheresTM ceramic microspheres, spheriglass m 3000e glass microspheres or goresil T M 1045 cristobalite. A process for producing a low gloss powder coating composition, comprising the steps of adding 5 to 60 wt based on the total weight of the low gloss powder coating composition, spheroidal particles having a median particle diameter greater than 10 microns and a maximum diameter of 50 microns to a powder coating composition comprising at least one resin selected from the group consisting of thermoplastic resins and thermosetting resins, wherein said spheroidal particles are selected from the group consisting of glass microspheres, ceramic microspheres, spheroidal minerals and metal microspheres.

280307.ck13210mut2clRima, 14 0o/s001l2 aIUMVI NVNZI1VO 88S 6S86 E 19+ XVa CSTI;T nHI OOZ EO/6z IO C 6. The process of claim 5 wherein the spheroidal particles have a median diameter greater than 15 microns. O S7. The process of claim 5 or 6 wherein said resin is selected from the group consisting of saturated polyesters, unsaturated polyesters, acrylic resins, acrylate C resins, polyester-urethanes, acrylic-urethanes, epoxy, epoxy-polyester, polyester- Cc acrylics, epoxy-acrylics, polyamides, polyvinylchloride, polyethylene, polyethylene c terephthalates, polybutylene terephthalate and polypropylene. l0 8. The process of any of claims 5 to 7 wherein said microsphere particles comprise W610, G800 or G850 zeeospheres T M ceramic microspheres, spheriglass TM 3000e glass microspheres or goresilTM 1045 cristobalite. 9. The coating composition of claim 1 substantially and as hereinbefore described with reference to the Examples. The process of claim 5 substantially as hereinbefore described with reference to the Examples. 11. A low gloss powder coating produced from the composition of any one of claims 1 to 4 or 9 or the process of any one of claims 5 to 8 or 16/1 /06.ckl3280nov9claims,15